Selection of automatic samplers to ensure sample integrity

Selection of Automatic Samplers to Ensure Sample IntegrityTraditional manual sampling techniques are often unacceptable for collecting wastewater samples for monitoring because of intricate routines required by permit or regulatory programs. Automatic samplers have resolved some issues about sample acceptability, but samplers offered in the marketplace differ in their ability to collect representative samples.Rick Sueverkruepp,lsco, Inc. Importance of
Collect and store aliquots that accurately reflect the composition of
Transport Velocity
Collect a sufficient volume to represent
accurate sample collection is the transport
velocity. Of the many techniques used by
differ in several ways, including intake
samples that incorrectly represent certain
design, constituents in the flow stream,
pollutants in the flow stream. Many studies
velocity of the flow stream, and transport
reflects the concentrations of pertinent
velocity. Additionally, differences spring
Table 1. Densities of
for a single purpose or special sampling
way that does not significantly alter the
Wastewater Pollutants
sampling sludges, high suspended solids, extreme depths, or difficult location
Material Specific
instrument selection process is a critical
laboratory procedures cannot Grit 1.2-1.7
used by automatic samplers today, some deliver samples that incorrectly represent certain pollutants in the
"capable of lifting a sample a vertical
Peristaltic Pump SampleManual SampleMean of 4-hr interval grab samplesVacuum Pump SampleBOD5 mg/LFigure 1.
line velocity of 0.6 to 3.0 m/sec. (2 to 10
even under experimental conditions — to
explains that "sample train velocities
variations in transport velocity are not
results are listed in Table 2, with averages
should exceed 2 fps" Both statements are
significant. In general, only researchers
samples are clearly because of the different
features of an ideal sampler, including that
techniques used to automatically collect
velocity adjustable from 0.61 to 3 m/sec
more closely reflect the values that are
analysis of loading effects These typically
generated collecting samples manually. The
are analyzed for BOD, COD, TSS and other
Kirkpatrick [4] that "minimum (suction
that contribute to these factors are almost
line transport) velocities of 2 to 3 feet per
differences in the sample values could be:
second would appear warranted." It is
velocity of 2 feet per second is required to
with a specific gravity of 2.65 and a friction
there would be less settling of solids during
factor of 0.025." This particle is sand.
transport to the storage containers. The
vertically, this particle would fall 0.61 m
during transport. If the suction line used is
representative sample. Transport velocity is
also not a factor when dissolved materials
would mean that the first 43.4 ml of the
are concerned. In actual application, it has
particles with these characteristics. If a
Intake velocities. The intake velocity of
would result in an understatement of the
The differences in the sampler's ability
to the intake velocity of the actual flow
to take a representative sample was most
transport velocity were raised to 3.0 fps,
clearly pointed out in Harris and Keffer's
concept of "iso-kinetic sampling" that
the error would be 2.9%. At 1 fps, the error
study. They noticed significant differences
in the results obtained from using different
These calculations seem to indicate that
types of samplers to sample the influent at
stream velocity are equal. It is theorized
and a lower speed peristaltic pump. These
velocity of 2 fps, and preferably 3 fps.
units were installed so they could collect
will not be forced into the intake line. A
samplers agree that it is very difficult —
stream. The intakes were tied together and
Reprinted from The National Environmental Journal, March/April 1996, Adams Trade Press, Atlanta, GA
Table 1. Comparison of Results from Two Samplers on the Same Flow StreamBOD5 COD NFS Test BOD5 COD NFSBOD5 COD NFS Average BOD5 COD NFS
line velocity well above the flow stream
volume to the sample container. After the
velocity at lower head heights. This can
cause a "scouring" of the channel floor
chamber. This allow solids to settle to the
collected from a "cloud" of settled out
material that artificially enriches the sample for suspended solids content and
ConclusionsReferences
and Quality Control," Water Environment
Operational differences in the samplers.
The samples collected by the peristaltic
consistently reflects the results observed
of liquid detectors and optical sensors,
accuracy and repeatability. The operator
collected samples data. Variations in the
sample to be collected and this volume is
then metered through a direct path to the
Samplers: What to Look for When Buying,"
For more information, contact the author, Rick Sueverkruepp, Isco, Inc., P.O. Box 82531, Lincoln, NE, 68501-2351;

Final Report – 2008-09 Research & Creative Works Grants Principal Investigator: Nicholas E. Burgis, Chemistry/Biochemistry Dept. Project Title: Developing a Less Toxic Chemotherapeutic Cocktail to Treat Multiple Myeloma. This report serves to document the scholarly research activities performed by the principal investigator and collaborators during the term of the Faculty Research Grant

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